1. Field of the Invention
The present invention relates to a power transmission device of an electric power steering apparatus. In particular, the present invention relates to a power transmission device of an electric power steering apparatus capable of reducing rattle noise generated as backlash increases due to wearing-out of a gear or generated due to impact transmitted from a road surface through a vehicle wheel and a steering shaft while improving a driver's steering feeling by reducing a locking feeling and a rotational resistance between a driving shaft of a motor and a gear shaft.
2. Description of the Prior Art
FIG. 1 is a partial sectional view illustrating a conventional power transmission device of an electric power steering apparatus.
As illustrated in FIG. 1, the power transmission device of an electric power steering apparatus includes a motor 130, a driving shaft 205, an inner rotor 220, an outer rotor 215, an elastic body 210, a first bearing 250, a worm shaft 235, a worm gear 245, a second bearing 270, a compression screw 255, a compression spring 265, and a gear housing 260.
The motor 130 has a driving shaft 205 extending to the outside of a motor housing, and a hollow outer rotor 215 is connected with the driving shaft 205 to be interlocked with each other.
The first bearing 250 and the second bearing 270 fix the worm gear 245 to a worm wheel gear 240 installed to a steering shaft 102.
The compression spring 265 supports the second bearing 270 configured to support the worm gear 245 toward the worm wheel gear 240 by the compression screw 255 and installed to the worm gear 245.
Accordingly, when the compression screw 255 is tightened, the compression screw 255 moves to contract the compression spring 265, and consequently, the worm gear 245 can be rigidly engaged with the worm wheel gear 240 by the compression force of the compression spring 265.
An inner rotor 220 is connected to the worm shaft 235, in which the inner rotor 220 is configured to be inserted into the outer rotor 215 connected with the driving shaft 205.
The power transmission device of an electric power steering apparatus configured as described above controls the driving of a motor by an electronic control unit provided in a vehicle according to a running condition of the vehicle, and the rotating force of the worm shaft generated by the driving of the motor is imparted to the rotating force of a steering wheel manipulated by a driver to be transmitted to a steering shaft so that the driver's steering status can be smoothened and stabilized.
However, the conventional power transmission device of an electric power steering apparatus has a problem in that manufacturing errors and assembly errors on the worm shaft and a coupling part of the motor shaft are accumulated such that the driving shaft of the motor and the worm shaft are not positioned coaxially, the locking feeling of the bearings occurs, and the rotating resistance of the worm shaft increases.
Further, when the durability of the worm and the worm wheel is advanced, a clearance occurs due to wearing-out, rattle noise occurs due to backlash, and an unpleasant feeling is caused to the driver at the time of manipulating a steering wheel due to rattle noise generated by impact transmitted from a road surface through a vehicle wheel and the steering shaft.